Is VPD important?

[The70’s]

Im building my grow room and educating myself as best i can. This seems important, and i want your ¢.02

Im going on multiple vacations this summer and weekend concerts, so no growing til the fall. Im not bragging just trying to keep the “put ur seeds in the soil” people from hijacking my threads
;0)

Theres three points of interest, seedlings, vegge, flower, and they all seem to be different needs, or hogwash, you tell me lol

 

[TorturedSoul]

Two hundredths of a cent? Well, you get what you pay for .

VPD has some significance. On the other hand, it is probably useful to know that people have been growing plants for (depending on who you ask, and what you consider to be evidence) at least 10,000, 12,000, or 23,000 years - and, on that sort of time scale, the concept is a recent one.

My opinion - you've already estimated its value, so take it for what it's worth - is that, in small-scale indoor gardening, it's more something to be aware of than something to get stressed about. Think about it... Most people have a relatively strong exhaust fan that constantly exchanges their garden's air. They also have one or more fan inside the garden space moving air around the plants and through the canopy. Plants have evolved mechanisms to regulate their own immediate environment. They bring moisture in via their root systems, and transpire it via the thousands of stomata (tiny pores, located mostly on the undersides of their leaves). Indoors, the gardener aids the process by using fans. Outdoors, natural wind does - a large oak tree can transpire 40,000 gallons of water per year, and an acre of corn transpires 3,000-4,000 gallons per day. This is an important process; the evaporation provides a cooling effect. Even when the relative humidity is, er, relatively high, the constant air exchange means that evaporation still takes place, because the air need only accept a small amount of additional moisture for it to occur (and then that ever-so-slightly damper air immediately gets sucked out of the garden space, and replaced with fresh air).

There are VPD charts floating around for people who feel that they do not have enough to worry about as it is (lol). But they're kind of generic, one-size-fits-all things. And, like everything else one-size-fits-all... it doesn't.

I grew using relatively large (approximately 23-gallon) single-plant DWC reservoirs for a while (and these were long growth phase SCROG setups, so assume pretty solid canopies of bud, six to eight square feet in area, each), and it was not uncommon to top them off in the morning, then return the same evening to find that 7 to 13 gallons had disappeared from each. Air was brought in from outside, through the garden spaces, and back out. Summers were hot (not "desert hot," but you wouldn't have wanted to be a roofer in August), sometimes muggy. Bud happened. . . .

 

[Emilya Green]

There are VPD charts floating around for people who feel that they do not have enough to worry about as it is (lol). But they're kind of generic, one-size-fits-all things. And, like everything else one-size-fits-all... it doesn't.

^^^ exactly!

 

[The70’s]

@TorturedSoul So its a sliding scale as long as my number falls somewhere inbetween during each stage, or as you say, “get close”

I think you were saying that Lol creating a nice balance, not a perfect one :0)

Thanx for you $.02

 

[CultivationArt]

It was a game changer for veg for me

 

[The70’s]

It was a game changer for veg for me

@CultivationArt

Tell me more, was it trouble maintaining the correct number ?

 

[CultivationArt]

@CultivationArt

Tell me more, was it trouble maintaining the correct number ?

Well for starters. I had no idea what the vpd or kpa was. I’d hear about it on educational videos but never applied the practice or science to my garden.


Now I do. And no. The number is not hard in a tent at least. I can keep a .8-1.2 kPa from start to late flower no problem with exhaust and a humidifier. Veg growth explodes. Need to stay on top of training otherwise it will bush out of control. Tbh yeah feed more evenly without burning themselves for over feeding due to a dry climate. And drought conditions are rare to come by because the humidity kinda keeps things afoot. I don’t recommend going off typed words. Because playing with your vpd can be dangerous if your in flower. But rather have someone show you in detail.

Seed to veg I maintain around 85-86F with a rh of 75%.

Then veg to early flower I run 85F with a rh of 68-72%. The. Flower I kinda throw that shit out the window

 

[The70’s]

Well for starters. I had no idea what the vpd or kpa was. I’d hear about it on educational videos but never applied the practice or science to my garden.


Now I do. And no. The number is not hard in a tent at least. I can keep a .8-1.2 kPa from start to late flower no problem with exhaust and a humidifier. Veg growth explodes. Need to stay on top of training otherwise it will bush out of control. Tbh yeah feed more evenly without burning themselves for over feeding due to a dry climate. And drought conditions are rare to come by because the humidity kinda keeps things afoot. I don’t recommend going off typed words. Because playing with your vpd can be dangerous if your in flower. But rather have someone show you in detail.

Seed to veg I maintain around 85-86F with a rh of 75%.

Then veg to early flower I run 85F with a rh of 68-72%. The. Flower I kinda throw that shit out the window

I found a Hydroponic store close by where im getting my “Goods” from, so my next visit i will ask, its a family run business, prices are fair and they are friendly folks, thanks for the input

 

[bluter]

vpd matters nothing until you have plants going. it's not something you can pre-set. the very presence of the plants changes the parameters, and it continues changing through the whole grow. shoot for a properly set up space, and the vpd will take care of itself.

I found a Hydroponic store close by where im getting my “Goods” from, so my next visit i will ask, its a family run business, prices are fair and they are friendly folks, thanks for the input

it's nice that you support the local, but those are usually the last place to get good advice. our FAQ is riddled with folk looking for help who were initially guided by what the hydro store told them.

 

[CultivationArt]

vpd matters nothing until you have plants going. it's not something you can pre-set. the very presence of the plants changes the parameters, and it continues changing through the whole grow. shoot for a properly set up space, and the vpd will take care of itself.






it's nice that you support the local, but those are usually the last place to get good advice. our FAQ is riddled with folk looking for help who were initially guided by what the hydro store told them.

Not pre set. No. But numbers and practices to follow.

I wish my tents guided themselves, but in the beginning I have to set my controllers and set my vents to the perfect opening. If I didn do anything. My vpd would be negative after every watering lol. Iv never heard of anyone saying it takes care of itself. That’s really cool. I’m not part of the cool kids club I guess lol. But I don’t mind the effort.

 

[bluter]

Iv never heard of anyone saying it takes care of itself.

meaning i grow through what i'm given. most of those charts are so wide that as long as your temps and rh are in range, your vpd follows. a lot of the charts themselves are useless, there are different ones that contradict each other. there is piles of debate around which chart to use etc, i just leave that to those who like to parse hairs.

there's only a couple of things that you can manipulate. i don't ignore the environment, i just don't stress over it.


edit : also i'm advocating for a properly set up grow space first and foremost. vpd and junk all comes later. get the space correct first, or you won't have a hope of effecting vpd anyway.

 

[Emilya Green]

I don't stress over it either. I try to use the central air to keep it under 90 in the grow room during the summer and I use space heaters in the winter to keep temps above 60. I live in Missouri where it can easily be 100% humidity during the summer and 20% humidity during the winter. I could add the extra costs to my grow by trying to regulate the RH in the grow rooms, but I have found that my plants grow well even if I don't adjust any of this. I just keep the air moving as best I can and leave it at that. For a significant cost in extra equipment and the running of it, I could do better and might even realize a bit more yield by maintaining the VPD... but for me, it just isn't worth the time, expense, and hassle of worrying about it.

 

[bluter]

I don't stress over it either. I try to use the central air to keep it under 90 in the grow room during the summer and I use space heaters in the winter to keep temps above 60. I live in Missouri where it can easily be 100% humidity during the summer and 20% humidity during the winter. I could add the extra costs to my grow by trying to regulate the RH in the grow rooms, but I have found that my plants grow well even if I don't adjust any of this. I just keep the air moving as best I can and leave it at that. For a significant cost in extra equipment and the running of it, I could do better and might even realize a bit more yield by maintaining the VPD... but for me, it just isn't worth the time, expense, and hassle of worrying about it.

i grow under even easier conditions than you. i could justify looking closer at vpd if i had your extreme rh. mine goes the other way, i'm drier. it is a bit easier to deal with low rh over high ... just turn the exhaust fan down a little. it is harder to move enough air to keep high rh in check.

 

[Skunksta]

Can’t lie. As already said vpd is another stresser.
Good air movement and keeping my room under 60% rh in flower is all I have ever needed.
Without my outtake fan on my rH no ladies 60/70 no fans running. Stick 3 ladies in
my space no fans running and it jumps to 80 plus.
Good outtake and intake when needed I say unless your in the middle
of summer and can’t turn your lights down don’t worry.
Most not all ladies I have grown in summer tend to deal with the extra
few C as long as I got air movement and fresh air coming in.

 

[bluter]

Can’t lie. As already said vpd is another stresser.
Good air movement and keeping my room under 60% rh in flower is all I have ever needed.
Without my outtake fan on my rH no ladies 60/70 no fans running. Stick 3 ladies in my space no fans running that’s jumps to 80 plus.
Good outtake and intake when need I say unless your in the middle of summer and can’t turn your lights down don’t worry.
Most not all ladies I have grown in summer tend to deal with the extra few C as long as I got air movement and fresh air coming in.

absolutely agree.

perfect conditions don't occur in nature either. although the thought of god running around the garden of eden with a vpd chart is worth the visual ..

 

[Skunksta]

Ps summer I also run 11pm to 11am can be a drama feeds but I have a drip system.

 

[bluter]

Ps summer I also run 11pm to 11am can be a drama feeds but I have a drip system.

i try to suspend indoor summer growing for at least 2 months at the height of summer. preferably i take 4. it's simply not worth fighting the conditions and pests. our summers are stupid short, and we work through the most of it, i like to enjoy what time i get without freaking about plants.

 

[Roy Growin]

i try to suspend indoor summer growing for at least 2 months at the height of summer. preferably i take 4. it's simply not worth fighting the conditions and pests. our summers are stupid short, and we work through the most of it, i like to enjoy what time i get without freaking about plants.

Same as that, I want to be done by June so I can enjoy the Summer, and the smoke
Then again, I said that last year but got itchy and put more seeds in... hard not to

 

[CultivationArt]

Iv also been studying using your vpd as a stressor, by using perfect conditions for weeks and fluctuations of drought and dryness during flower. But iv never tried this. And scared as hell to even attempt it. I do drought here and there for a good wet dry cycle. But moisture in the air going to dry makes me worry of PM.

 

[bluter]

Same as that, I want to be done by June so I can enjoy the Summer, and the smoke
Then again, I said that last year but got itchy and put more seeds in... hard not to

almost always do the exact same. i have a tendency to do long running sativas which doesn't help. and i like to do a seed run then a clone run right after to reduce costs. i really only get 2 - 3 grows a yr in.

i do a load of med based stuff like topicals and pills. plus my smoke. i'm supplying 3 adults so far just fine on 2 - 3 grows max. but it can get a bit thin at times. we took 8 months off this yr as health issues precluded using my flower room, but we've come through it not bad at all. the flower room is only 4 x 4 so i'm not growing massive amounts of plants.

Iv also been studying using your vpd as a stressor, by using perfect conditions for weeks and fluctuations of drought and dryness during flower. But iv never tried this. And scared as hell to even attempt it.

it's really only a soil thing. there's loads of stressors that folk have applied in flower over the years. they kinda come and go like a fad. i've been at it long enough not to give a shit.

after a while everyone i know who is a decent grower is the same.

I do drought here and there for a good wet dry cycle.

a good wet / dry cycle is not the same as droughting. when i did hp type i found it ok to let them go a bit drier once in a while, but it was not a practice.

if i had lockout or issues i would dry them out, then flush hard with plain water and h202. then feed in 48hrs with corrected nutes. it's gold if you get your nute balance correct. the only time it can't help is in the very back part of flower if you've lost too many fans already.

But moisture in the air going to dry makes me worry of PM.

pm sucks. that is all air movement though. if you can get enough wind on them and have decent exhaust you can conquer pm. i have to watch for pm, my flower space could use some better circulating fans.